Device for low-temperature separation of air

ABSTRACT

The device serves for the cryogenic separation of air. It has the following features: a main heat exchanger and a supercooling countercurrent heat exchanger ( 2 ); a distillation column system for nitrogen-oxygen separation ( 5 ), which comprises a high-pressure column and a low-pressure column; a mixing column ( 1 ); means for introducing charge air via the main heat exchanger into the high-pressure column and into the mixing column; a liquid-oxygen line for introducing liquid oxygen from the low-pressure column into the upper region of the mixing column; an oxygen product line for extracting oxygen gas from the upper region of the mixing column through the main heat exchanger. The mixing column ( 1 ) and at least one of the two heat exchangers mentioned ( 2, 6 ) are arranged in a common cold box ( 3 ).

The invention relates to a device for low-temperature separation of air according to the preamble of claim 1.

Air separation methods with mixed columns have been known since the 1970s (DE 2204376=U.S. Pat. No. 4,022,030). In addition, such methods are disclosed in U.S. Pat. No. 5,454,227, U.S. Pat. No. 5,490,391, DE 19803437 A1, DE 19951521 A1, EP 1139046 B1 (=US 2001052244 A1), EP 1284404 A1 (=U.S. Pat. No. 6,662,595 B2), DE 10209421 A1, DE 10217093 A1, EP 1376037 B1 (=U.S. Pat. No. 6,776,004 B2), EP 1387136 A1 and EP 1666824 A1. These documents show only schematic process diagrams and contain no information on the spatial arrangement of the mixed column relative to the other parts of the apparatus.

From DE 19904526 A1, it is known to arrange high-pressure columns, low-pressure columns and mixed columns beside one another on the base. In U.S. Pat. No. 6,167,723, it is also recommended to set up the mixed column on the base; here, the low-pressure column is arranged above the mixed column, and the high-pressure column stands next to it. Also, in DE 19919587 A1, the mixed column stands on the base; the double column that consists of the high-pressure column and the low-pressure column is constructed above the mixed column.

The object of the invention is to find an improved arrangement of the mixed column.

This object is achieved in that the mixed column and at least one of the two above-mentioned heat exchangers are arranged in a shared coldbox.

A coldbox is used for thermal insulation of system parts (see, for example, Hausen/Linde, Tieftemperaturtechnik [Low-Temperature Technology], 1985, in particular pages 490 and 491). A “coldbox” is defined here as an insulating jacket, which comprises a heat-insulated interior space complete with outer walls; system parts that are to be insulated, for example one or more separation columns and/or heat exchangers, are arranged in the interior space. The insulating action can be produced by corresponding configuration of the outer walls and/or by the filling of the intermediate space between system parts and outer walls with an insulating material. In the latter variants, preferably a powdery material, such as, for example, perlite, is used.

For the device according to the invention, there are three preferred variants:

-   -   Mixed column, main heat exchanger, and subcooling countercurrent         device in a shared coldbox     -   Mixed column and subcooling countercurrent device in a shared         coldbox;

main heat exchanger in another, separate coldbox

-   -   Mixed column and main heat exchanger in a shared coldbox;         subcooling countercurrent device in another separate coldbox.

The invention relates in particular to the first two variants, whereby the mixed column preferably is arranged above the subcooling countercurrent device.

All data regarding spatial orientation relate here to the orientation of the device during the operation of the columns.

A container (for example, a column or a heat exchanger) is located “above” (or “below”) another container when its lower edge (upper edge) is located on a higher (lower) geodetic level than the upper edge (lower edge) of the other container. In this case, a vertical line that goes through both containers can but should not exist. In the projection on a horizontal plane, the cross-sections of the two containers can overlap, but they can also be arranged completely offset to one another. The term “above one another” is defined analogously.

In the embodiment of the invention described here, the—otherwise unused—space above the heat exchanger is used in an advantageous way by the mixed column being placed there. An especially compact device is produced.

In the invention in principle, the high-pressure column, the low-pressure column, and the main heat exchanger can be arranged in one or more additional coldboxes. In an extreme case, in each case they have a separate coldbox; in another case, they are housed in a shared coldbox with a mixed column and subcooling countercurrent device (with or without a main heat exchanger), which in particular encloses all cold parts of the device, in this device, i.e., also the main heat exchanger.

The subcooling countercurrent device is used to subcool or to heat up one or more liquids from one of the columns of the distilling-column system for nitrogen-oxygen separation or the mixed column in the countercurrent to form one or more cold, gaseous streams, which in general come from the low-pressure column. In particular, in a subcooling countercurrent device, liquid streams that are depressurized at the boiling point from a column with higher pressure (for example, the high-pressure column) into a column with lower pressure (for example, the low-pressure column) are cooled as much as possible up to the boiling point, which corresponds to the lower pressure level. In this case, the amount of vapor (flash) during the depressurization from higher pressure to lower pressure is minimized. When the liquid oxygen is sent from the low-pressure column through the subcooling countercurrent device before injection into the mixed column, the liquid oxygen is conversely heated up to get as close as possible to the boiling point under the—usually higher—pressure of the mixed column. Counter to this, the cold streams are heated up to the dewpoint of the columns with the lower pressure. Since these streams go into the main heat exchanger, the process air in the high-pressure column is also hotter, i.e., it is nearer the dewpoint. The proportion of the preliquefied air is minimized. In the previously known mixed-column systems, the space above this heat exchanger remains largely unused, not so in the embodiment of the invention described here. In this variant of the invention, the subcooling countercurrent device is produced by a component that is separate from the main heat exchanger.

In this case, the mixed column can be fastened by suitable connecting elements to the subcooling countercurrent device. As an alternative (or preferably if the mixed column is arranged laterally offset to the subcooling countercurrent device), the mixed column is arranged on a frame, optionally with additional support on the outer wall of the coldbox or on other devices, which are enclosed by the coldbox. This frame is preferably supported on the base of the coldbox. Although the double column from the high-pressure column and the low-pressure column is arranged in the same coldbox, it may be especially advantageous if the mixed column is supported on the double column.

It is advantageous when a shared coldbox encloses a mixed column, subcooling countercurrent device, high-pressure column and low-pressure column. The coldbox preferably has a rectangular base area. The main heat exchanger in principle can also be housed in the shared coldbox. As an alternative, it is arranged in a second, separate coldbox, in particular when the latter can be pre-fabricated, and then is transported to a large extent completely to the construction site. High-pressure columns and low-pressure columns are preferably configured as double columns.

The first and last variants mentioned above can be produced in such a way that the mixed column and the main heat exchanger are arranged in the shared coldbox. In this connection, it is advantageous when a first coldbox encloses the main heat exchanger and the mixed column. A second coldbox then contains the high-pressure column and the low-pressure column of the distilling-column system for nitrogen-oxygen separation, which preferably are arranged in the form of a conventional double column. In this variant of the invention, the subcooling countercurrent device can be integrated into the main heat exchanger. In small systems, all above-mentioned cold parts can be arranged in a single coldbox. This can be useful even in the case of very large systems, in which the coldbox is assembled on the construction site.

In this case, it is advantageous when a first coldbox encloses the main heat exchanger and the mixed column, and a second coldbox encloses the high-pressure column and the low-pressure column.

The high-pressure column and low-pressure column are preferably arranged above one another.

The invention as well as further details of the invention are explained in more detail below based on the embodiments that are depicted in the drawings. Here:

FIG. 1 shows a first embodiment of the invention with an arrangement of a mixed column and subcooling countercurrent device above one another in a horizontal cross-sectional view,

FIG. 2 shows the first embodiment in a vertical cross-sectional view,

FIG. 3 shows a second embodiment of the invention with an arrangement of a mixed column and main heat exchanger in a shared coldbox in a horizontal cross-sectional view, and

FIG. 4 shows the second embodiment in a vertical cross-sectional view.

In the example of FIG. 1, a mixed column 1 and a subcooling countercurrent device 2 are arranged in a shared coldbox 3. High-pressure columns and low-pressure columns of the distilling-column system for nitrogen-oxygen separation are produced as a conventional double column 5 and are also housed in the coldbox 3. FIG. 2 shows the same arrangement in another view.

In the two drawings, only the outer side walls of the coldbox 3 are shown. Details such as pipelines, valves, and the interior of the devices 1, 2, and 5 are not shown. The intermediate space between the devices 1, 2, and 5 and the outer wall of the coldbox 3 is filled with perlite. The bottom of the coldbox 4 is formed by a separate outer wall. The double column 5 is supported by a frame, not shown, on the base 4 of the coldbox 3. The mixed column 1 and the subcooling countercurrent device are supported by connecting elements on the double column 5, also not shown.

A main heat exchanger is housed in the first embodiment in a separate coldbox (not shown in FIGS. 1 and 2).

The two dotted circles la and lb in FIG. 1 represent two variations on the first embodiment, in which the mixed column is arranged offset to the subcooling countercurrent device 2. The mixed column, however, is also arranged here above the subcooling countercurrent device (analogously to FIG. 2); to reach this geodetic height, it must be mounted on a separate frame.

In the example of FIG. 3, a mixed column 1 and a main heat exchanger 6 are arranged in a shared coldbox 3. FIG. 4 shows the same arrangement in another view. In the two drawings, only the outer side walls of the coldbox 3 are shown. Details such as pipelines, valves, and the interior of the devices 1, 6 are not shown. The intermediate space between the devices 1, 6 and the outer wall of the coldbox 3 is filled with perlite. The bottom of the coldbox 4 can be formed by a separate outer wall or a foundation. The two devices 1, 6 are supported by one frame each.

A subcooling countercurrent device and the distilling-column system for nitrogen-oxygen separation are housed in one or more separate coldboxes in the second embodiment (not shown in FIGS. 3 and 4). 

1-7. (canceled)
 8. A device for low-temperature separation of air with a main heat exchanger (6), and a subcooling countercurrent device (2), with a distilling-column system for nitrogen-oxygen separation (5), which has a high-pressure column and a low-pressure column, and with a mixed column (1) and with means for introducing charging air via the main heat exchanger into the high-pressure column and into the mixed column, with a liquid oxygen line for introducing liquid oxygen from the low-pressure column into the upper area of the mixed column and with an oxygen product line for drawing off oxygen gas from the upper area of the mixed column by the main heat exchanger, whereby the mixed column (1) and the subcooling countercurrent device (2) are arranged in the shared coldbox (3), the mixed column (1) is arranged above the subcooling countercurrent device (2), which encloses the shared coldbox (3), the mixed column (1), the subcooling countercurrent device (2), the high-pressure column, and the low-pressure column, and the high-pressure column and the low-pressure column are arranged above one another (5).
 9. The device according to claim 8, wherein the mixed column (1) is arranged on a frame.
 10. The device according to claim 8, wherein the mixed column (1) and the main heat exchanger (6) are arranged in the shared coldbox (3).
 11. The device according to claim 8, wherein the high-pressure column and low-pressure column, on the one hand, and the mixed column, on the other hand, are arranged beside one another. 